UNIVERSITY PARK — Although many wild birds carry Salmonella, the strains of the bacteria they convey mostly do not harbor antimicrobial-resistance genes, according to Penn State researchers, who led a team conducting a new, nationwide study.
That’s good news, according to team leader Ed Dudley, professor of food science.
“While we’ve known for a while that wild birds can carry Salmonella, the strains they carry appear to be of lesser concern to human health,” he said. “The assumption was that these Salmonella — like the bacteria we can isolate from domesticated farm animals — would carry large numbers of antimicrobial-resistance genes. We found the opposite to be true.”
Wild birds are known to be common reservoirs of Salmonella enterica, a pathogen that sickens millions of people every year, Dudley explained, and scientists have worried that wild birds carrying antimicrobial-resistant Salmonella enterica pose a risk to public health because they can spread the resistant bacteria across large areas in a short time. This research indicates that wild birds do not serve as important reservoirs of resistant Salmonella enterica strains.
To reach their conclusion, researchers whole-genome sequenced 375 Salmonella enterica strains from wild birds collected in 41 U.S. states from 1978 until 2019 to examine bacterial resistance to antibiotics and heavy metals. The study — which was spearheaded by Yezhi Fu, a postdoctoral researcher in Dudley’s research group in the College of Agricultural Sciences — answers important questions about the role migrating birds play in transmitting diseases to humans.
“We worked with the National Wildlife Health Center because it has this genetically amazing collection of Salmonella isolates collected over more than 40 years from sick migratory birds,” Dudley said. “It is an opportunistic collection for us, and somebody just needed to analyze it. It yielded information we couldn’t have gotten anywhere else.”
“To find what antibiotics a particular Salmonella strain is resistant to, we don’t have to run the traditional lab-based tests anymore — where you grow it on some type of media, expose it to antibiotics and it either grows or it doesn’t,” Dudley said. “Now, we can sequence the entire genome, and by identifying certain gene markers, we can predict — with almost perfect precision — what antibiotics the organism will be resistant to.”
The U.S. Food and Drug Administration and the U.S. Department of Agriculture supported the study.
